The invention relates rollers in general and more particularly to an improved method and apparatus for controlling line pressure in the type of roller which includes a hollow cylinder revolving about a stationary cross head.
There are quite a number of roller designs with revolving hollow cylinder and stationary cross head, in which the distribution of the line pressure can be controlled to a certain extent. To obtain the distribution of line pressure, these rollers have support elements which are distributed along the interior of the hollow cylinder. The support elements act between the cross head and the hollow cylinder and transmit forces from the cross head to the inside circumference of the hollow cylinder. The support elements are braced against the cross head which is deflected within the hollow cylinder. The support elements, at the same time, supply forces required to generate the line pressure. To bring about differences in the line pressure, the support elements are controlled differently.
In U.S. Pat. No. 3,119,324, piston-cylinder units are lined up along the cross head and act against support shoes which are braced against the inside circumference of the hollow cylinder via an oil film. The pressure fed to the individual piston-cylinder units can be controlled differently. In DE-OS No. 22 30 139, the support shoes have, on the side facing the inside circumference of the hollow cylinder, chambers which are supplied with pressure fluid from the cylinder space of the piston-cylinder units via choke holes, so that the support shoes are supported, at least partially, hydrostatically and the forces are transmitted to the inside circumference via the pressure fluid contained in the chambers.
In DE-PS No. 14 61 066, finally, the cross head contains a longitudinal slot in which several strip-like pistons are accommodated one behind another, which push sliding shoes against the inside circumference of the hollow cylinder. The pressure fluid pressure of the pistons can be controlled separately.
In the above-mentioned embodiments, the line pressure is controlled at support elements which at the same time also provide the overall line pressure. Another roller is described in DE-AS No. 23 32 861. In this roller the hollow cylinder is spaced from the cross head leaving an annular space therebetween which is divided into longitudinal chambers by longitudinal seals disposed between the cross head and the cylinder. One chamber is on the side of the roller gap and the other roller gap is filled with pressure fluid. The pressure in one of the chambers is varied in zones formed therein so that the pressure in the zones differs from that in the rest of the chamber. Thus, part of the line pressure is provided by the pressure fluid contained in the longitudinal chamber. Superimposed on this pressure is the pressure of support elements corresponding to those of the aforementioned DE-OS No. 22 30 139, which are located in the interior of the longitudinal chamber facing the roll gap and which can be controlled separately, so that an additional controlled component is superimposed on the substantially uniform pressure component of the longitudinal chamber.
Here, too, however, the sole thought is to affect the line pressure by influencing a number of discrete, separately controlled support elements which participate simultaneously in the formation of the line pressure.
For controlling the line pressure in this manner, it is necessary to control the entire number of relatively high pressures separately. The individual support elements require these high pressures since they must contribute to providing the line pressure.
If the line pressure distribution is changed and especially, if the entire line pressure level is changed, a large number of high pressures must be readjusted. The precise control of many pressures of that magnitude requires a substantial amount of equipment.
It is thus an object of the present invention to reduce the amount of equipment required for line pressure control in a roller of the type mentioned above.